FIG. 10 is a block diagram showing the structure of a processing time measurement device such as the one depicted in Non-Patent Document 1. The processing time measurement device shown in FIG. 10 is structured with a network interface (network I/F) 1001, a Ping message transmission section 1002, a Ping message transmission time record section 1003, a Pong message reception time record section 1005, and a processing time calculation section 1004.
With the processing time measurement device shown in FIG. 10, the Ping message transmission section 1002 transmits a Ping message at an arbitrary time via the network I/F 1001. The Ping message transmission time record section 1003 records the transmission time at which the Ping message is transmitted by the Ping message transmission section 1002. The Pong message reception time record section 1005 records the reception time of the Pong message received via the network I/F 1001. The processing time calculation section 1004 compares the transmission time of the Ping message with the reception time of the Pong message, and takes the difference thereof as call processing time of an SIP server or the like that is a measurement object.
Note that a message transmitted from a measurement main body towards the measurement object is called a Ping message. A message returned from the measurement object when the Ping message arrives at the measurement object is called a Pong message. That is, the Ping message is a special message that is returned from the measurement object. Typically, the Ping message is structured by including an instruction to return a response for the message explicitly or structured to cause an error so that an error message is returned.
The measurement main body can detect the active/inactive state of the measurement object by receiving the Pong message. Further, the measurement main body judges the measurement time that is a difference between the transmission time of the Ping message and the reception time of the Pong message as the propagation time of the network and the processing time in the measurement object. Assuming that the propagation time of the network is so short that it can be ignored, the measurement time can be considered equal to the processing time in the measurement object. That is, the processing time of the measurement object can be measured by using the Ping message and the Pong message.
As shown in FIG. 11, the Ping message is transmitted to a neighboring node (e.g., a relay server such as an SIP server which communicates with the measurement main body in the network). In a case shown in FIG. 11, node A is the measurement main body, and node B neighboring to the node A is the measurement object. The node B that is the neighboring node performs reception processing of a message. In the reception processing, the node B reads out processing information from a header part of the message, and identifies whether or not to return the message. When judged that it is necessary to return the message, a message is returned as a Pong message. The Ping message can designate a return node. That is, it is also possible to designate the node to which the Pong message is to be transmitted in accordance with the Ping message.
Non-Patent Document 1 shows an example which implements Ping messages with ICMP (Internet Control Message Protocol) and Pong messages with ICMP ECHO REPLY. With SIP (Session Initiation Protocol), it is known to form Ping messages by properly setting transferable-number parameters called “MaxForwards”. When “MaxForwards” reaches “0”, transfer cannot be done any more. As a result, an error message is to be returned. This error message is used as a Pong message.
Non-Patent Document 1: W. Richard Stevens “TCP/IP Illustrated, Volume 1” Addison-Wesley Publishing Company, 1994, pp. 85-96